<!DOCTYPE html>
<html>
<head>
	<title>05大致结构</title>
<style>
	#a {
		width: 800px;
		height: 200px;
		background: gray;
	}

	#b {
		width: 800px;
		height: 200px;
		background: green;
	}

	#c {
		width: 800px;
		height: 200px;
		background: blue;
	}
</style>
</head>
<body>
	<div id="a"></div>
	<div id="b"></div>
	<div id="c"></div>
</body>
</html>